The present invention relates to an infrared emitter and, and more particularly, a method and apparatus for increasing the output of an infrared emitter.
Infrared emitters provide radiant heat in numerous applications. For instance, they are the preferred heat source for drying paints supplied to metal surfaces, including solvent based paints, water based paints, and powder paints. They also provide heat for environmental test chambers and many industrial processes.
A typical infrared emitter includes a slender tubular quartz enclosure containing an elongated coiled filament that extends through the enclosure and connects to lead-in conductors at opposite ends of the enclosure. Infrared radiation emanates from the filament in all directions in a spherical pattern, and thus the power of the radiant energy decreases in proportion to the square cube of the distance from the emitter. Only the energy which is absorbed by the object is transferred to the object as heat energy, and of the energy which strikes the object, a portion will be reflected, a portion will be absorbed, and depending upon the object, a portion may be transmitted through the object. Only the radiant energy which actually strikes the object and is absorbed provides heat within the object. The remaining radiant energy is redirected or continues travelling through space, thereby reducing the overall energy transfer efficiency from the infrared emitter to the object to be heated.
To improve the radiant energy transfer efficiency, the radiant energy leaving the emitter is generally focused in some manner towards the object to be heated. In one approach the infrared emitters are employed within an enclosed tubular sheath having reflective walls. The energy not directly passing from the infrared emitter to the object and absorbed by the object, continues to be reflective off the surfaces of the chamber until it strikes the object, escaping from an opening in the chamber or dissipating through inefficiencies and the reflectors.
In another application, where the heating chamber must be kept free of articulate matter and cleanliness is essential, the heating chamber of the infrared emitter is constructed using flat walls. This reduces the amount of dust that can form on the external reflectors of the infrared emitter.
In yet another application, a gold reflective coating has been placed on the outer surface of the infrared emitter forming an integral reflector. This feature included with the aforementioned flat wall construction, provides an advantage of improving the radiant energy transfer efficiency and at the same time improving the cleanliness and the heating chamber environment. However, the gold reflective coating places restrictions upon the infrared emitter design. A gold metal reflector coating may simply vaporize off of the surface of the enclosure due to excessive emitter temperature caused by trapped energy within the emitter system.
In still yet another application, an external sheath of quartz or other high transmissive material has been placed about the infrared emitter enclosure, with a reflective metal coating applied to the outer sheath. U.S. Pat. No. 5,382,805 addressed an infrared energy emitter which included a longitudinally extending tubular enclosure infrared energy transmitting material enclosing a longitudinally extending filament. A longitudinally extending outer tubular sheath of infrared energy transmitting material covered the tubular enclosure and was provided with a reflector. This allowed the infrared emitter to run at high power densities while maintaining a relatively cool outer surface temperature. However, higher power densities adversely affect the end seals and reflective coatings. The aforementioned patent tried to overcome this high temperature concern by providing fluid conductive filters at each end of the sheath to filter cooling fluid paths through the emitter. However, the ability to cool the infrared emitter by passing a cooling fluid into the enclosure at one end does not efficiently reduce the high temperature concerns with the integrity of the emitter while attempting to improve the radiant energy transfer efficiency.
It is therefore a principle object of the present invention to provide a method for increasing the output power of an infrared emitter without sacrificing the structural integrity of the emitter. The high temperature concerns associated with the higher power density of the emitted infrared energy are addressed by more efficient heat venting techniques.
It is still another object of the present invention to provide a longitudinally extending hermetically sealed tubular enclosure of infrared energy transmitting material enclosing the filament having at least one inner tubular support device in a predetermined position including a plurality of apertures for fluid flow therethrough.
It is yet another object of the present invention to provide a heat sink which is intimately associated with an electrical conductor extending from the filament out through the tubular enclosure which encapsulates the emitting filament. The heat sink is used to assist in heat dissipation from the infrared emitter and the filament electrical supply conductor, typically a pin.
It is still yet another object of the present invention to provide a longitudinally extending outer tubular sheath of infrared energy transmitting material having an inner and an outer surface with a plurality of ports strategically located at predetermined locations along the outer surface of the sheath. The sheath will have two ends, each end will have at least one passage for fluid flow therethrough. A reflector, comprising a reflective coating on a surface of the sheath, will extend partially circumferentially with the sheath forming a central longitudinal section for the transmission and/or absorption of secondary electromagnetic wave emission.
A heat dissipator comprising a high or low emissivity coating and is disposed over the reflector forming an intimate contact thereto. This also aids in adjusting the temperature of the infrared emitter by strategically and controlled radiant means.
It is still another object of the present invention to provide that the ports be placed in the window of the outer tubular enclosure to direct the exhausted fluid toward the work in process. Alternatively, the ports can be placed so that the fluid will be channeled away from the work in process. The ports also provide pressure relief to accommodate fluid flow into one or both ends of the emitter system.
It is still another object of the present invention to provide high watt densities from small outer tubular diameters while simultaneously cooling the integral reflector material, the outer tubular enclosure, the reflector, and the window. The higher power output capabilities will reduce the overall quantity of emitters required for many systems without reducing the overall system output power while providing increased efficiency.
It is yet another object of the present invention to create different radiation emission patterns by varying the cross-sectional tubular enclosure shape. These shapes may also be combined with other shapes to include a mixture of polygons.
It is yet another object of the present invention to provide an inner tubular support positioned in a predetermined location with respect to the sheath. In addition to its support function, the inner tube support may include passages to permit the flow of the cooling fluid through the inner support. This may allow fluid flow passages configured to achieve a predetermined fluid flow pattern.
It is yet another object of the present invention to provide dual peak wavelengths of infrared emission efficiently from one infrared emitter. This may be accomplished with or without the use of a transducer housing.
It is still yet another object of the present invention to provide selectable electromagnetic peak wavelength emissions.
The present invention relates to an apparatus and method for increasing the output power of an infrared emitter and addressing the concerns associated with the damaging and undesirable higher temperatures produced within the electromagnetic emitter components. The apparatus and method of the present invention use unique reflection and heat dissipation techniques to accomplish the aforementioned.
In a preferred embodiment of the invention, the apparatus of the present invention includes a method for heating an object with infrared energy by passing a current through an elongated filament, and may be disposed within an hermetically sealed cylindrical enclosure. Surrounding the enclosure is an outer elongated tubular sheath of infrared energy transmitting material having an inner and an outer surface with a plurality of ports strategically located at predetermined locations along the outer surface of the sheath. The sheath has two ends, and each end has at least one passage for fluid flow therethrough. There is a reflective coating on an inner surface of the sheath extending partially, circumferentially with the sheath to form a central longitudinal section referred to as a window. A coating of predetermined emissivity is disposed on the outside of the sheath and is generally congruent to the reflective coating that resides on the inner surface. The central longitudinal section of the sheath is spaced apart from the enclosure about the entire circumference of the enclosure sufficiently to protect the reflective coating from the infrared energy that is emitted by the filament. Infrared radiation from the filament is reflected off of the reflective coating on the sheath, back toward the filament, thus passing infrared radiation towards an object from the filament through the window. A cooling fluid passes through the space between the sheath and the enclosure to cool the enclosure, sheath, the reflective coating and controlled emissivity coating.